In a typical Universal Serial Bus (USB) power circuit, a single voltage source supplies voltage to multiple USB outputs. As such, if USB devices are connected with the multiple USB outputs, each of these USB devices are drawing current from the same voltage source. While an ideal voltage source may be able to always output a constant voltage, real-world voltage sources cannot output an ideal constant voltage at least when the load connected with the voltage source changes rapidly.
For example, if a first USB device is connected with a first USB power output and is receiving current from the voltage source, the overall load connected with the voltage source may change when a second USB device is connected with another USB power output. This increase in load may result from the second USB device drawing current from the same voltage source. Upon initial connection to a USB power output, the second USB device may draw an inrush current due to components (e.g., capacitors) requiring initial charging, thus resulting in a transient electrical load on the voltage source. Due to the transient load caused by the second USB device being connected to the second USB power output, the voltage supplied to the first USB device may “droop.” Such droop refers to a temporary decrease in the provided voltage. Such a temporary decrease in output voltage may affect the performance of the first USB device and/or may violate a defined standard that specifies a minimum voltage that a USB device should be supplied. The more isolated each output is from each other output, the less the amount of droop in supplied voltage may be present.
Conventionally, in order to decrease such droop (and increase isolation) when a second USB device is coupled with the same voltage source, each USB power output may be connected with some number of capacitors. Such capacitors may help reduce the amount of voltage droop when the load on the voltage source is increased by supplying current when the voltage output by the voltage source decreases. In a typical arrangement, each USB power output may be connected with a substantial number of capacitors, such as eight 10 μF capacitors, a 100 μF capacitor, and a 0.1 μF capacitor.
Use of such numbers of capacitors may have drawbacks. For example, if a large number of capacitors are used, the cost associated with acquiring the capacitors may be substantial, especially if a large number of circuits containing the USB power circuit are being manufactured. Further, the more capacitors used, the more circuit board space that is occupied and unavailable for other components. As such, a circuit board may need to be enlarged to accommodate all of the capacitors and/or other components may not be added to the circuit board because of the space needed for the capacitors.